perf: cache compiled regex patterns in prometheus metrics filtering (#3825)

Signed-off-by: Keiven Chang <keivenchang@users.noreply.github.com>

components/src/dynamo/common/utils/prometheus.py

@@ -13,7 +13,8 @@ while Dynamo runtime metrics are available immediately after component creation.
 
 import logging
 import re
-from typing import TYPE_CHECKING, Optional
+from functools import lru_cache
+from typing import TYPE_CHECKING, Optional, Pattern
 
 from prometheus_client import generate_latest
 
@@ -72,6 +73,30 @@ def register_engine_metrics_callback(
     endpoint.metrics.register_prometheus_expfmt_callback(get_expfmt)
 
 
+@lru_cache(maxsize=64)
+def _compile_exclude_pattern(exclude_prefixes: tuple[str, ...]) -> Pattern:
+    """Compile and cache regex for excluding metric prefixes.
+
+    Args take tuple not list - lru_cache requires hashable args (tuples are hashable, lists are not).
+    """
+    escaped_prefixes = [re.escape(prefix) for prefix in exclude_prefixes]
+    prefixes_regex = "|".join(escaped_prefixes)
+    return re.compile(rf"^(# (HELP|TYPE) )?({prefixes_regex})")
+
+
+@lru_cache(maxsize=64)
+def _compile_include_pattern(metric_prefix: str) -> Pattern:
+    """Compile and cache regex for including metrics by prefix."""
+    escaped_prefix = re.escape(metric_prefix)
+    return re.compile(rf"^(# (HELP|TYPE) )?{escaped_prefix}")
+
+
+@lru_cache(maxsize=128)
+def _compile_help_type_pattern() -> Pattern:
+    """Compile and cache regex for extracting metric names from HELP/TYPE comment lines."""
+    return re.compile(r"^# (HELP|TYPE) (\S+)(.*)$")
+
+
 def get_prometheus_expfmt(
     registry,
     metric_prefix_filter: Optional[str] = None,
@@ -107,21 +132,18 @@ def get_prometheus_expfmt(
         if metric_prefix_filter or exclude_prefixes or add_prefix:
             lines = []
 
-            # Build exclude pattern for lines to skip entirely
+            # Get cached compiled patterns
             exclude_line_pattern = None
             if exclude_prefixes:
-                escaped_prefixes = [re.escape(prefix) for prefix in exclude_prefixes]
-                prefixes_regex = "|".join(escaped_prefixes)
-                # Match lines starting with: HELP/TYPE comments OR metric lines with excluded prefixes
-                exclude_line_pattern = re.compile(
-                    rf"^(# (HELP|TYPE) )?({prefixes_regex})"
-                )
+                exclude_line_pattern = _compile_exclude_pattern(tuple(exclude_prefixes))
 
             # Build include pattern if needed
             include_pattern = None
             if metric_prefix_filter:
-                escaped_prefix = re.escape(metric_prefix_filter)
-                include_pattern = re.compile(rf"^(# (HELP|TYPE) )?{escaped_prefix}")
+                include_pattern = _compile_include_pattern(metric_prefix_filter)
+
+            # Get cached HELP/TYPE pattern
+            help_type_pattern = _compile_help_type_pattern()
 
             for line in metrics_text.split("\n"):
                 if not line.strip():
@@ -139,7 +161,7 @@ def get_prometheus_expfmt(
                 if add_prefix:
                     # Handle HELP/TYPE comments
                     if line.startswith("# HELP ") or line.startswith("# TYPE "):
-                        match = re.match(r"^# (HELP|TYPE) (\S+)(.*)$", line)
+                        match = help_type_pattern.match(line)
                         if match:
                             comment_type, metric_name, rest = match.groups()
                             # Remove existing prefix if present